Sound: from noise to communication
H-M. Voipio(1), E. Björk(2), M. Hakumäki(3), T. Nevalainen(4).
(1) Laboratory Animal Centre, University of Oulu, Oulu; (2) Department of
Environmental Sciences; (3) Department of Physiology; (4) National Laboratory
Animal Center, University of Kuopio, Kuopio, Finland
Animals in laboratory animal facilities are surrounded by sounds.
The acoustic environment consists of sounds from equipment controlling
environment and from animal care. Furthermore, animals produce sounds
themselves by moving
or banging the cages and also by vocalising.
Continuous white noise sound exposure has been shown to have an effect on
animal's physiology and behaviour. In some situations environmental sounds
can become harmful to animals. In an animal facility, a wide variety of
different sound pitch range from low to very high frequencies occur.
Likewise, sound pressure levels vary from low background level, <35
dB (lin), to high levels caused by animal care, for example cage
changing, >70-80 dB (lin) or dog barking, 90-100 dB (lin).
In addition to
intensity, type of the sound is important. Fear reactions of rats are
stronger to noise type sound than to harmonic or pure tones, and sound
structure may be even more significant than sound intensity. In animal
units, a typical noise type is caused by running tap water, whereas rat's
ultrasonic vocalisation is a tone type sound.
While assessing acoustic environment, hearing sensitivity is essential, and
differs between species. Many laboratory rodent species hear high frequency
sounds, ultrasounds, inaudible to man, but low frequency hearing is poor.
Furthermore, hearing ability changes during life, and there are also strain
differences. Therefore, when effects of either environmental or
experimental sounds are studied, the correct method to account for auditory
sensitivity is the use of species specific sound pressure level weighting.
More precise spectral analysis should be used to reveal if the sound is
inaudible to each of the species within certain frequency range.
Moreover,there are differences in response of animals in different status.
reactions to sound of pregnant and mother rats are weaker compared to those
of non-pregnant females, while young adult rats are the most sensitive.
However, there seems to be no need to provide them with a different
Vocalisation is also a constituent of the sound world. In addition to
audible, rodents emit ultrasounds during fighting and reproductive
behaviour, between mother and pups and while afraid or in pain. The impact
of acoustic environment on vocalisation is unclear, but it has been
suggested that ultrasounds can disturb communication. It is, however,
important to realise that acoustic environment of a cage is different from
that of an animal room, since ultrasounds attenuate even at short distances.
The optimal acoustic environment of animals remains unknown. Based on the
fear reactions of rats, sudden high frequency noise type, and other sounds
at high intensity should be avoided in animal care. As an example, if the
rat is removed to clean cage before topping the feedhopper, the sound
intensity in the rat's ear is much higher than if the rat would stay in the
dirty cage. In some units, whole time background sound has been used to
mask those produced by care. Yet, background sound pressure level cannot be
raised high enough for this purpose. Therefore, it would be more advisable
to change the working routines.
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